High Performance Air Filters Produced from Freeze-Dried Fibrillated Wood Pulp: Fiber Network Compression Due to the Freezing Process

High efficiency air filters to capture submicrometer particles have been produced from fibrillated pulp fiber by a wet beating and freeze-drying procedure. Under appropriate conditions, air permeability and particle capture efficiency meeting the N95 standard can be achieved. Pulp type, beating time, and the freezing process were examined. Particle capture efficiency improved with increased beating, but excessive beating resulted in the formation of a low permeability layer (LPL). This LPL was the result of fiber network compression induced by the freezing process and formed farthest from the cold source. Adding a formation aid commonly used in paper making prevented compression of the fiber network, resulting in higher quality filters.